Expandable intervertebral cage

ABSTRACT

An expandable intervertebral cage device includes a first base plate and a second base plate, a proximal block with internal threading that mechanically couples the first base plate and the second base plate, and a distal block comprising an internal passage. The device has exactly two arm assemblies, one on each side. Each arm assembly includes a first arm mechanically coupled to the first base plate and the distal block, and a second arm is mechanically coupled to the second base plate and the distal block. A screw is arranged partially within the internal threading of the proximal block and passes through the internal passage of the distal block, such that rotation of the screw relative to the proximal block causes a change in distance between the proximal block and the distal block, and a corresponding change in the spacing and lordosis of the device.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/585,544, filed Dec. 30, 2014, which in turn is acontinuation in part of U.S. patent application Ser. No. 14/242,451,filed Apr. 1, 2014, now U.S. Pat. No. 8,940,049, which are incorporatedherein by reference in its entirety. This application is also related toPCT Application No. PCT/US2014/052913, filed Aug. 27, 2014.

TECHNICAL FIELD

The present invention relates to the distraction and fusion of vertebralbodies. More specifically, the present invention relates to devices andassociated methods for distraction and fusion of vertebral bodies thatremain stable when implanted and facilitate fusion following their usefor distraction to aid in the correction of spinal deformity by reducinga collapsed disc and establishing sagittal alignment, lordosis, orkyphosis.

BACKGROUND

The concept of intervertebral fusion for the cervical and lumbar spinefollowing a discectomy was generally introduced in the 1960s. Itinvolved coring out a bone graft from the hip and implanting the graftinto the disc space. The disc space was prepared by coring out the spaceto match the implant. The advantages of this concept were that itprovided a large surface area of bone to bone contact and placed thegraft under loading forces that allowed osteoconduction and inductionenhancing bone fusion. However, the technique is seldom practiced todaydue to numerous disadvantages including lengthy operation time,destruction of a large portion of the disc space, high risk of nerveinjury, and hip pain after harvesting the bone graft.

Presently, at least two devices are commonly used to perform theintervertebral portion of an intervertebral body fusion: the first isthe distraction device and the second is the intervertebral body fusiondevice, often referred to as a cage. Cages can be implanted asstandalone devices or as part of a circumferential fusion approach withpedicle screws and rods. The concept is to introduce an implant thatwill distract a collapsed disc and decompress the nerve root, allow loadsharing to enhance bone formation and to implant a device that is smallenough to allow implantation with minimal retraction and pulling onnerves.

In a typical intervertebral body fusion procedure, a portion of theintervertebral disc is first removed from between the vertebral bodies.This can be done through either a direct open approach or a minimallyinvasive approach. Disc shavers, pituitary rongeours, curettes, and/ordisc scrapers can be used to remove the nucleus and a portion of eitherthe anterior or posterior annulus to allow implantation and access tothe inner disc space. The distraction device is inserted into thecleared space to enlarge the disc space and the vertebral bodies areseparated by actuating the distraction device. Enlarging the disc spaceis important because it also opens the foramen where the nerve rootexists. It is important that during the distraction process one does notover-distract the facet joints. An intervertebral fusion device is nextinserted into the distracted space and bone growth factor, such asautograft, a collagen sponge with bone morphogenetic protein, or otherbone enhancing substance may be inserted into the space within theintervertebral fusion device to promote the fusion of the vertebralbodies.

Intervertebral fusion and distraction can be performed through anterior,posterior, oblique, and lateral approaches. Each approach has its ownanatomical challenges, but the general concept is to fuse adjacentvertebra in the cervical thoracic or lumbar spine. Devices have beenmade from various materials. Such materials include cadaveric cancellousbone, carbon fiber, titanium, and polyetheretherketone (PEEK). Deviceshave also been made into different shapes such as a bean shape, footballshape, banana shape, wedge shape, and a threaded cylindrical cage.

U.S. Pat. Nos. 7,070,598 and 7,087,055 to Lim et al. disclose minimallyinvasive devices for distracting the disc space. The devices includescissor-jack-like linkages that are used to distract a pair of endplatesassociated with adjacent vertebra from a first collapsed orientation toa second expanded orientation. A pull arm device is used to deliver anddistract the device in the disc space. However, the device is primarilyused for distraction and not subsequent vertebral fusion. The devicewould not work as a fusion device, because once the pull arm isdisconnected from the device, the device will not be stable enough tomaintain proper spacing of the vertebrae until fusion can occur. Theendplates of the device are also solid and do not permit bone growth forsuccessful fusion.

U.S. Patent Publication No. 2008/0114367 to Meyer discloses a devicethat uses a scissor-jack-like arrangement to distract a disc space. Tosolve the instability problem of the scissor-jack arrangement, a curablepolymer is injected to fill the disc space and the distraction device isdisabled from attempting to support the load. The curable polymer anddisabling of the device are necessary because the device could notadequately support the distracted disc space. The base plates of thedevice have at least two or more degrees of freedom, collectively, in adistracted position and are therefore not stable under the loadsencountered supporting the disc space. Absent injection of the polymer,and the support and control supplied by the implanting physician via theremovable distraction tool, the base plates would collapse, which couldcause severe damage to the vertebral bodies.

Accordingly, there is a need in the art for a device that can distractadjacent vertebral bodies in a minimally invasive manner while providingstable support for the disc space during fusion; particularly, a devicethat would allow for angular orientation of the base plates to bematched exactly to the unique alignment, or desired alignment, of apatient's spine.

SUMMARY OF THE DISCLOSURE

According to an embodiment, an expandable intervertebral cage deviceadapted to be implanted into an intervertebral disc space in a patient'sbody. The device includes a first base plate having a first outerbearing surface configured to interface with a first vertebra of theintervertebral disc space, a second base plate having a second outerbearing surface configured to interface with a second vertebra of theintervertebral disc space, a proximal block mechanically coupled to thefirst base plate and the second base plate, wherein the proximal blockcomprises internal threading, a distal block comprising an internalpassage, and exactly two arm assemblies, wherein a first one of the twoarm assemblies is arranged on a first side of the device and a secondone of the two arm assemblies is arranged on a second side of thedevice, wherein each of the exactly two arm assemblies comprises a firstarm mechanically coupled to the first base plate and the distal blockand a second arm is mechanically coupled to the second base plate andthe distal block. A screw is arranged partially within the internalthreading of the proximal block and passing through the internal passageof the distal block, such that rotation of the screw relative to theproximal block causes a change in distance between the proximal blockand the distal block, and a corresponding change in the spacing andlordosis of the device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIGS. 1A-1B are perspective views of an expandable intervertebral cagedevice according to an aspect of the present invention.

FIG. 1C is a side view of the expandable intervertebral cage deviceaccording to the embodiment of FIGS. 1A-1B.

FIG. 1D is a cross-sectional view of the intervertebral cage deviceaccording to the embodiment of FIGS. 1A-1C, taken along line 1D-1D ofFIG. 1A.

FIGS. 2A-2B are perspective views of an expanded intervertebral cagedevice according to an embodiment.

FIG. 2C is a side view of the expanded intervertebral cage device ofFIGS. 2A-2B.

FIG. 2D is a cross-sectional view of the intervertebral cage deviceaccording to the embodiment of FIGS. 2A-2C, taken along line 2D-2D ofFIG. 2A,

FIG. 3 is a perspective view of an end plate, according to anembodiment.

FIG. 4 is a perspective view of a side arm, according to an embodiment.

FIG. 5 is a perspective view of a ring pin, according to an embodiment.

FIG. 6 is a perspective view of a proximal block, according to anembodiment.

FIG. 7 is a perspective view of a distal block, according to anembodiment.

FIG. 8 is a perspective view of a pin, according to an embodiment.

FIG. 9 is a perspective view of a rod, according to an embodiment.

FIG. 10A is a rear view of an embodiment of an expandable intervertebralcage device according to an aspect of the present invention;

FIG. 10B is a side view of an embodiment of an expandable intervertebralcage device according to an aspect of the present invention;

FIG. 10C is a top view of an embodiment of an expandable intervertebralcage device according to an aspect of the present invention;

FIG. 11 is a perspective view of an embodiment of an expandableintervertebral cage device according to an aspect of the presentinvention;

FIG. 12A is a perspective view of an embodiment of a first base plateaccording to an aspect of the present invention;

FIG. 12B is a perspective view of an embodiment of a second base plateaccording to an aspect of the present invention;

FIG. 12C is a side view of an embodiment of a base plate according to anaspect of the present invention;

FIG. 13 is a perspective view of an embodiment of an arm according to anaspect of the present invention;

FIG. 14 is a perspective view of an embodiment of first, second andthird blocks according to an aspect of the present invention;

FIG. 15 is a perspective view of an embodiment of a pin according to anaspect of the present invention;

FIG. 16 is an exploded view of an embodiment of an expandableintervertebral cage device according to an aspect of the presentinvention;

FIGS. 17A-17B are side and perspective views an embodiment of anexpandable intervertebral cage device according to an aspect of thepresent invention in a distracted state, wherein the nose portion isfurther distracted that the rear portion;

FIGS. 18A-18B are side and perspective views an embodiment of anexpandable intervertebral cage device according to an aspect of thepresent invention in a distracted state, wherein the rear portion isfurther distracted that the nose portion;

FIGS. 19A-19B are side and perspective views of an embodiment of anexpandable intervertebral cage device according to an aspect of thepresent invention in a distracted state, wherein the rear portion andnose portion are substantially equally distracted;

FIG. 20 is a simplified view of an embodiment of an expandableintervertebral cage device according to an aspect of the presentinvention.

FIGS. 21A-21B are schematic representations of a pair of adjacentvertebral bodies.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention.

DETAILED DESCRIPTION

In the following detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, one skilled in the artwill recognize that the present invention may be practiced without thesespecific details. In other instances, well-known methods, procedures,and components have not been described in detail so as to notunnecessarily obscure aspects of the present invention. U.S. Pat. No.8,628,577, invented by the inventor of the present application,discloses a stable intervertebral body fusion and distraction device.This patent is hereby incorporated herein by reference in its entiretyother than the summary of the invention, claims and any expressdefinitions set forth therein.

FIG. 1A is a perspective view of expandable intervertebral cage device10, as seen from a distal end. FIG. 1B shows the same intervertebralcage device 10 from an opposite, proximal end. As shown in FIGS. 1A and1B, intervertebral cage device 10 is in a collapsed position. FIG. 1C isa side view of the intervertebral cage device 10 in the collapsedposition, and FIG. 1D is a cross-sectional view of the intervertebralcage device 10 taken across the cross-section line 1D-1D shown in FIG.1A. FIGS. 2A-2D are counterparts to FIGS. 1A-1D showing the sameintervertebral cage device 10. However, in FIGS. 2A-2D, while the viewsof intervertebral cage device 10 are the same as their respectivecounterparts in FIGS. 1A-1D, device 10 is in a fully expandedconfiguration rather than the collapsed position. FIGS. 3-9 depictindividual elements or parts of device 10 in isolation and in moredetail.

Intervertebral cage device 10 includes first base plate 12 and secondbase plate 14. On each side (i.e., each edge perpendicular to both thebase plates 12 and 14 and the proximal/distal axis), intervertebral cagedevice 10 includes a first arm 16, second arm 18, screw 19, severalrings 20, distal block 22, proximal block 24, pins 26, and rods 28. Thehidden side of the device 10, not visible in the perspective viewsherein, comprises many substantially similar structures to thosedescribed with reference to the numbered elements. Intervertebral cagedevice 10 is a device that can be used to hold two structures, such asthe vertebrae of a spine, in a fixed spatial relationship with respectto one another. As will be described with respect to subsequent figures,device 10 can be expanded to hold structures in any fixed spatialrelationship with a range of distances and angles with respect to oneanother. Device 10 provides desirable spacing and lordosis and can beoperated using a single screw, as described below, to achieve commonlyused intervertebral spacing and lordosis levels. In contrast to themultiple-screw devices described above, the user of a single screwdevice reduces the complexity and increases the mechanical strength ofthe device. In some embodiments, at full extension the device 10 canexhibit about 23° of lordosis, for example, which is greater than acommonly used angle for many intervertebral devices.

As shown in more detail with respect to FIG. 3, first base plate 12,which is substantially similar to second base plate 14, comprisestextured surface 30, arm socket 32, and rod passage 34. First base plate12 is a portion of device 10 that comprises a bearing surface. As usedthroughout this disclosure, “bearing surface” refers to the outsidesurface of a base plate (e.g., 12, 14) that interfaces with the endplateof a vertebra, other bone, or other structures that are to be held in afixed spatial relationship from one another. Textured surface 30 cancomprise, for example, any texture that promotes bone growth to hold thebase plate 12, or which provides grip or traction when compressedagainst bone. Arm socket 32 is usable to provide a mechanical connectionbetween base plate 12 and a corresponding structure, such as first arm16, as depicted in FIGS. 1A-1D and 2A-2D. Similarly, rod passage 34 canbe used to facilitate a mechanical connection between base plate 12 anda corresponding structure, such as proximal block 24, as described inmore detail below.

As shown in FIGS. 1A-1D and 2A-2D, base plates 12 and 14 are arranged onopposite from one another in device 10, and can be positioned within arange of distances and angles relative to one another, depending on theextent of the expansion of device 10. For example, as shown with respectto FIGS. 1A-1D the device 10 is in a collapsed position, and base plates12 and 14 are relatively close to one another, and arrangedsubstantially parallel to one another. In the configuration shown withrespect to FIGS. 2A-2D, the base plates 12 and 14 are relatively furtheraway from one another on the distal end, and are angled relative to oneanother (this angle is sometimes referred to as lordosis). Inembodiments, the extent of lordosis and/or distance between variousparts of the base plates 12 and 14 can vary. In some embodiments, baseplates can each be angled at 23 degrees. In this embodiment, aproximalend of each base plate can remain at a generally constant distance fromeach other as the device is expanded about pins 28 (with perhaps aslight change in distance as the plates rotate about pins).

Referring now to FIG. 4, the mechanism by which device 10 is expanded orcollapsed is shown, and in particular first arm 16. First arm 16, whichis substantially similar to second arm 18, includes body portion 36,first connector 38, and second connector 40. A substantially similarpair of arms to first arm 16 and second arm 18 are included in device 10on the side that is not depicted in the perspective views previouslyshown. Body portion 36 extends between first connector 38 and secondconnector 40. The distance between first connector 38 and secondconnector 40 determines in part the extent to which the base plates 12and 14 of FIGS. 2A-2D can be distanced from one another, and the anglebetween them. First connector 38 and second connector 40 can each berotatably connected to an adjoining structure. So, for example, as shownwith respect to FIGS. 1A-1D and 2A-2D, first connector 38 can beconnected to first plate 12 or second plate 14 via a pin 26. Likewise,second connector 40 can be connected to distal block 22. The connectionsspace the parts from one another, while allowing relative rotationbetween them.

Referring now to FIG. 5, ring 20 is depicted, which can also supportinterconnection between the base plate 12 and the distal block 22 viaany of the arms. In particular, ring 20 holds pin 26 (shown in moredetail with respect to FIG. 8) such that it passes through both firstbase plate 12 and first connector 38 of first arm 16. In operation, theeffects of lateral forces (i.e., forces perpendicular to theproximal-distal directions previously described) are mitigated by ring20. Ring 20 can prevent some types of relative lateral movement betweenfirst base plate 12, first arm 16, and pin 26. Ring 20 does this bysnapping into groove 52 of pin 26, as described in more detail withrespect to FIG. 8.

Referring now to FIG. 6, distal block 22 is shown in perspective. Distalblock 22 includes internal passage 42, first bearing 44, and secondbearing 46. Internal passage 42 is configured to provide a passage for aportion of screw 19, as shown previously with respect to FIG. 1D andFIG. 2D. In some embodiments, the portion of screw 19 that passesthrough internal passage 42 is a shank (i.e., unthreaded), or else theinternal passage 42 itself is unthreaded, or both, such that there isnot co-rotation between distal block 22 and screw 19. Screw 19 passesthrough internal passage 42 in the embodiment shown in FIGS. 1A-1D and2A-2D, and as such the distal block 22 and screw 19 are fixed relativeto one another in the proximal/distal directions. As described in moredetail below with respect to FIG. 7, rotation of screw 19 can causescrew 19 to advance in either the proximal or distal direction, whichthereby causes a corresponding movement of the distal block 22 in thesame direction. As can be seen in the figures, screw 19 can define afirst diameter at proximal block that is greater than a second diameterat distal block. The diameter of screw at the interface with distalblock can be the same or greater than that at proximal block to preventthe screw from advancing distally through distal block. A ring 20 canprevent the screw 19 from being pulled proximally through the distalblock.

First bearing 44 and second bearing 46 can receive a portion of anotherobject, such as first arm 16 and second arm 18 as shown in FIGS. 1A-1Dand 2A-2D. First arm 16 and/or second arm 16 can rotate relative tofirst bearing 44 and/or second bearing 46, while remaining mechanicallyfixed to one another. As described above, rotation of screw 19 can causemovement of distal block 22 in the proximal or distal direction. Thisresults in corresponding displacement of the second connector 40 of thefirst arm 16 (and the corresponding structure in the second arm 18).

FIG. 7 is a perspective depiction of proximal block 24. Proximal block24 includes internal threads 48 and rod passage 50. Internal threads 48can be configured to interact with an adjacent component, such as screw19 as shown in FIGS. 1D and 2D. Proximal block 24 is connected to firstbase plate 12 and second base plate 14 by rods 28. As shown in FIGS.1A-1D and 2A-2D, rod 28 connects first base plate 12 with proximal block24. Rod 28 can pass through rod passages 50 and 34 so that the proximalblock 24 is mechanically coupled to first base plate 12 while allowingthe base plates (12, 14) to rotate relative to the blocks (22, 24).

FIGS. 8 and 9 depict the connection structures between the first baseplate 12 and adjoining structures. In particular, FIG. 8 depicts a pin26 that connects the first base plate 12 to the distal block 22 via thearms, and FIG. 9 depicts a rod 28 that connects the first base plate 12to the proximal block 24. Pin 26 further includes groove 52 which canhold ring 20, as previously described.

In operation, first arm 16 and second arm 18 are rotatable and areconnected to first base plate 12 and second base plate 14, respectively.Because the structural connection between first base plate 12 and screw19 is substantially similar to the structural connection between secondbase plate 14 and screw 19, only the former will be described herein indetail. First base plate 12 is mechanically coupled via pins 26 to firstarm 16 via arm socket 32. First arm 16 and second arm 18 are also eachmechanically coupled to screw 19 through distal block 22. In all, thisconnection permits for first base plate 12 to be indirectly connected tothe screw 19 while still permitting relative rotation between them.Together with rings 20, distal block 22, proximal block 24, and pins 26,a mechanical interconnection is formed between each of the base plates12 and 14 that can be adjusted by an external tool (not shown). Rods 28provide a pivot point that results in a specific relationship betweenthe amount of extension of the device 10 and a relative angle betweenthe first base plate 12 and the second base plate 14.

An external tool (not shown) can be used to turn screw 19, via head 29.Because proximal block 24 is internally threaded (as shown in moredetail with respect to FIG. 7), rotation of screw 19 causes relativemovement of the screw 19 with respect to the proximal block 24. Bycontrast, distal block 22 is not internally threaded. Rather, distalblock 22 and screw 19 are connected such that movement of screw 19 ineither the proximal or distal directions (i.e., the direction in whichscrew 19 moves relative to proximal block 24 when rotated) causes acorresponding movement of the distal block 22. This can be accomplishedas shown, for example, in FIG. 2D, where distal block 22 is pushedand/or pulled by screw 19, and the interconnection is made by a springor clamp on one side holding the distal block 22 against a flange on thescrew 19. In alternative embodiments, various other interconnectionsbetween the screw and block can be made, which will result inco-movement in the proximal or distal direction without co-rotation. Asdistal block 22 is moved by screw 19, it forces movement of first arm 16and second arm 18.

As screw 19 is rotated, due to the internal threading of proximal block24, the distance between the distal block 22 and proximal block 24changes. As the distance between distal block 22 and proximal block 24increases, the arms 16 and 18 are caused to rotate. First arm 16 andsecond arm 18 rotate as the device 10 is converted from a collapsedconfiguration, such as that shown in FIGS. 1A-1D, to an expandedconfiguration, such as that shown with respect to FIGS. 2A-2D. Thisrotation results in increased distance between the first base plate 12and the second base plate 14, as well as increased lordosis. Asdescribed with respect to other embodiments below, rotating screw 19 tochange the distance between first base plate 12 and second base plate14, as well as changing the amount of lordosis, can be useful to provideintervertebral support.

The embodiment shown in FIGS. 1A-1D, 2A-2D, and 3-9 provides suchintervertebral spacing, support, and lordosis with a relativelystraightforward mechanical structure. The device 10 can be implanted ina compact configuration, then expanded to the appropriate size and angleby rotating screw 19, causing the changes in angle and spacingpreviously described, as desired.

Referring to FIGS. 10A-10C and FIG. 11, there can be seen an expandableintervertebral cage device 100 according to an aspect of the presentinvention. Device 100 includes a device body 102. Device body 102 caninclude a nose portion 104, a rear portion 106, a pair of opposed baseplates 108 having outer bearing surfaces 107, and a plurality of armassemblies 110. Schematic representations of a pair of adjacentvertebral bodies 10 are depicted in FIGS. 21A-21B. Each arm assembly 110can include a pair of opposed arms 112 hingedly attached to each other,with each opposing arm 112 hingedly attached to one of the base plates108. In one embodiment, device 100 can include three arm assemblies 110a, 110 b, and 110 c, extending crosswise from first side 116 of device100 to second side 118 of device 100. In one embodiment, opposing arms112 of arm assemblies 110 a, 110 b, and 110 c are pivotally coupled to ablocks 122 a, 122 b, and 122 c with pins 114. Block 122 a can bepositioned nearest the rear portion 106, block 122 c can be positionednearest the nose portion 104, and block 122 b can be positioned betweenblocks 122 a and 122 c.

Referring to FIGS. 12A-12C, in one embodiment, base plates 108 caninclude a first, or top, base plate 108 a, with a top bearing surface107 a configured to interface with an end plate of a superior vertebraof the intervertebral disc space, and a second, or bottom, base plate108 b having a bottom bearing surface 107 b configured to interface withan end plate of an inferior vertebra of the intervertebral disc space.In one embodiment, each base plate 108 can include one or more openings124 to facilitate bone growth through the device 100. Openings 124promote vertebral fusion because bone can grow directly through thedevice 100. Although depicted as being generally rectangular, opening124 can comprise any shape. Alternatively, a generally solid surface ora surface with multiple openings can be provided on each base plate 108.

Base plates 108 can have a rough surface or teeth 109 to create frictionwith the base plates of the vertebra to prevent accidental extrusion ofthe device 100 or to promote bone growth for successful fusion. Baseplates 108 or other elements of the device can also in some embodimentsbe made compliant for exaggerated non-uniform distraction whilemaintaining the stability of the device 100. Nose portion 104 can betapered to facilitate insertion of the device 100 into the disc space.Rear portion 106 can also be tapered. In one embodiment, base plate 108can include a plurality of bores 105. Each bore 105 can be sized toaccept a portion of opposing arm 112 to facilitate a hinged coupling.

In one embodiment, device 100 can have a total of twelve arms 112 (fourarms for each arm assembly 110 a, 110 b, and 110 c, with two arms ofeach assembly on each side of the device). In one embodiment, all of thearms 112 can be substantially identical. Referring to FIG. 13, each arm112 can include a protrusion 113 sized to fit into one of the bores 105of base plate 108 to facilitate a hinged coupling. In one embodiment,arms 112 can be welded to base plates to prevent failure. Each arm 112can include a bore 115 sized to accept a pin 114 for coupling the arm112 to a block 122.

In one embodiment, device can have a total of three blocks—a first orproximal block 122 a, a second or central block 122 b and a third ordistal block 122 c. Referring to FIG. 14, in one embodiment, central anddistal blocks 122 b and 122 c can be substantially identical. Each block122 can be defined by two side bores 128 sized to accept pin 114 for thepurpose of coupling two arms 112 to block 122. In one embodiment, sidebores 128 can be substantially parallel to one another. Each block 122can also be defined by two longitudinal bores 126, each sized to acceptan actuation member 120. In one embodiment, each longitudinal bore 126can be threaded. In another embodiment, only one longitudinal bore 126of each block 122 is threaded. In one embodiment, longitudinal bores 126can be substantially parallel to one another. In one embodiment,longitudinal bores 126 can be orthogonal to side bores 128. Proximalblock 122 a can be adapted to attach to an insertion device forinserting device 100 into the disc space. In one embodiment, side slots125 of proximal block 122 a can be configured to receive portions ofinsertion device.

In one embodiment, device 100 can include a total of six pins 114.Referring to FIG. 15, each pin 114 can be substantially cylindrical inshape and have opposing ends 127 sized to fit into bore 115 of arms 112on opposing sides 116, 118 of device 100. Pins can be sized to extendthrough side bore 128 of block 122 between opposing arms 112, for thepurpose of pivotably coupling two arms 112 to a given block 122. In oneembodiment, pin 114 can include notches 129. Notches 129 can be sized toallow clearance for actuation members 120 through longitudinal bores126, thereby allowing each arm assembly 110 to be more compact. In oneembodiment, pin 114 can include a slot 131 proximate each end 127 of pin114 sized to accept a snap ring 133 (shown in FIG. 16) that sits outsideof arms to lock pins in place. In one embodiment, a distal portion ofone or more actuation members 120 can have a larger diameter than theremainder of actuation member. Longitudinal bores 126 would therefore belarger to accommodate this larger section of the screw.

Referring to FIG. 16, in one embodiment, device 100 can include a firstactuation member 120 a and a second actuation member 120 b. In oneembodiment, actuation members 120 a and 120 b can be substantiallyidentical. In one embodiment, actuation member 120 can include athreaded portion 135 of a diameter sized to threadedly couple withlongitudinal bore 126 of one or more blocks 122. Actuation member 120can include a second non-threaded portion 136 having a smaller diameterthan threaded portion 135. One end of actuation member 120 can bedefined by a slot or socket 138 structured to receive a tool for drivingactuation device 120. In one embodiment, socket 138 can be capable ofreceiving a hex key or Allen wrench, for example, for rotatably drivingactuation device 120. In one embodiment, actuation member 120 caninclude a slot 137 proximate one end of actuation member 120 sized toaccept snap ring 139 that can lock actuation members in axial positionrelative to blocks. Alternatively, snap ring 139 can be located at theproximal end of block 122 c, which provides further stability to thescrew and reduces the stress on the snap ring.

In one embodiment, first actuation member 120 a can extend through firstarm assembly 110 a into second arm assembly 110 a. For example, firstactuation member 120 a can be threadedly coupled to first arm assembly110 a and rotationally coupled to second arm assembly 110 b. Secondactuation member 120 b can extend through second arm assembly 110 a intothird arm assembly 110 c. For example, second actuation member 120 a canbe threadedly coupled to second arm assembly 110 b and rotationallycoupled to third arm assembly 110 c.

As shown in FIGS. 17A-17B, in one embodiment, actuation of firstactuation member 120 a in a first direction drives blocks 122 a and 122b closer together, which causes expansion of arm assemblies 110 a and110 b and distraction of base plates 108. As shown in FIGS. 17A-17B,actuation of second actuation member 120 b in a first direction drivesblocks 122 b and 122 c closer together, which causes expansion of armassemblies 110 a and 110 b and distraction of base plates 108.

First actuation member 120 a and second actuation member 120 b arecapable of being actuated independently of each other. This independentactuation allows for angular orientation of the base plates 108 to bematched exactly to the unique alignment, or desired planar alignment, ofadjacent vertebrae of a patient's spine. Examples of various possibleangular orientations of base plates 108 in the distracted state can beseen at FIGS. 17A-17B. Such angulations can be done when the device isexpanded within the disc space, enabling the device to go betweenlordotic and kyphotic angles while in the disc space so that the surgeoncan adjust as needed to correct the deformity based on observations madeduring the procedure.

Conversely, actuation of first actuation member 120 a in the oppositedirection drives blocks 122 a and 122 b apart, thereby bringing baseplates 108 closer together. Likewise, actuation of second actuationmember 120 b in the opposite direction drives blocks 122 b and 122 capart, thereby bringing base plates 108 closer together. Thisback-drivability of the device 100 is helpful for sizing the device 100and removing the device 100 if necessary, such as in the event ofpost-surgical infection, trauma, or failure to fuse.

Referring again to FIG. 16, non-threaded portion 136 of actuation member120 and its respective rotational coupling to block 122 enable device100 to allow for additional distraction due to in-vivo axial tension.For example, the rotational coupling can be constructed with sufficientclearance to allow block 122 b to temporarily slide closer to 122 a, orblock 122 c to temporarily slide closer to block 122 b. However, havingdistracted slightly under tensile loading the device would return to theoriginal height as compressive loading is returned. The parallelismwould remain unchanged, while lordotic endplates may undergo a smallangular displacement that would return to the set lordosis with thereapplication of the normal compressive loading. This extensibility ofdevice 100 could offer great benefits to the fusion process as theendplates, which may be growing into the endplates of the vertebralbodies, would not be pulled away from the endplates by motion of thepatient's spine, damaging early bone growth.

In another embodiment, in place of non-threaded portion 136 and snapring 139, portions of the actuation member 120 can be reverse threadedto allow distraction without changing the position of the threadedmembers along the respective axes of the threaded members helping tokeep the device from adversely interacting with the anatomy of thepatient.

In various embodiments, device body 102 is shaped to be ergonomic.Device body 102 can have various shapes, such as, for example,rectangular or kidney-shaped. A kidney-shaped device body 102 maximizescontact between the device and the vertebral bodies because the baseplates of vertebrae tend to be slightly concave. One or both ends of thedevice may also be tapered to facilitate insertion. This minimizes theamount of force needed to initially separate the vertebral bodies. Inaddition, the device may be convex along both its length and its width,or bi-convex. Device body can also be comprised of various materials.Such materials can include, for example, titanium, steel. PEEK, carbonfiber and cobalt chromium. The device can also be constructed in varioussizes depending on the type of vertebra and size of patient with whichit is being used, for example, specifically for an anterior lumbarinterbody fusion, oblique or a laterlal interbody fusion. In someembodiments, the threaded member 120 can be micro-machined or splitalong its length and reconnected using a bellows or flexible torquetransmission device, to be able to operate through an angle that may benecessitated by the shape of the device.

In one embodiment, a locking mechanism can be utilized to preventrotation of the threaded members to ensure the device remains in thedistracted state. In one embodiment, the locking mechanism can beactivated with the insertion device. In one embodiment, locking may beenhanced by tightening a threaded nut (not shown) against one or more ofthe blocks 122.

As is demonstrated by a simplified form of device 100 shown in FIG. 20,device 100 can stably support the disc space because it has negative onedegree of freedom once locked in the distracted position with actuationmembers 120 in place. From Gruebler's equation, the number of degrees offreedom=3*(n−1)−2f, where n is the number of links in the linkage and fis the number of one degree of freedom kinematic pairs in the linkage.As is shown in FIG. 20, the device 100 has 10 links and 14 kinematicpairs, so 3*(10−1)−2*14=−1 degrees of freedom. The device is thereforeactually over constrained (meaning that there are additional constraintsbeyond the minimum necessary to make it stable), and stable underloading conditions. This allows device 100 to stably support the discspace upon distraction. In some embodiments, a crush surface orcompliant materials may be used in concert with structure to minimizehysteresis that may be present in the device and due to clearance in armassemblies 112 necessary for overcoming the over-constraint in deviceshaving fewer than zero degrees of freedom due to redundant constraints.

In operation, device 100 can be placed between adjacent vertebrae orvertebral bodies and used to distract the endplates of the adjacentvertebral bodies and subsequently serve as a fusion device. One or moreinsertion tools (not depicted) can be used to insert and distract device100. Referring to FIGS. 10A, 10B and 11, the device body 102 can be seenin its initial compressed configuration. In FIGS. 17A-19B, device body102 is in various expanded configurations. The insertion tool can beconnected to actuation members 120 with the proximal block 122 a andfirst used to insert device 100 into a desired location. Device 100 canbe inserted with tapered nose portion 104 first. One device 100 can beinserted, or, for additional support, two devices 100 can be inserted.Two devices 100, each sized to be inserted within one-half of theevacuated disc space, can be especially useful for treating largerpatients in which the device may encounter higher loads. In anotherembodiment, three or more small devices can be inserted into the discspace in order to very accurately control the orientation and distancebetween the discs. Three or more distraction mechanisms may bepositioned circumferentially between two circular endplates to result invery accurate control and orientation of the base plates. Such a devicewould resemble a hexapod.

To distract device 100, an insertion tool can be used to rotateactuation members 120 in a first direction. Actuation of threaded member120 a in a first direction drives blocks 122 a and 122 b closertogether, which causes distraction of base plates 108. Likewise,actuation of threaded member 120 b in a first direction drives blocks122 b and 122 c closer together, which causes distraction of base plates108. Actuation of threaded members 120 a and 120 b in the oppositedirection respectively drives blocks 122 a and 122 b and blocks 122 band 122 c apart, thereby bringing base plates 108 closer together.

Once base plates 108 are distracted to a desired degree, insertion toolscan be disconnected from threaded members 120 and the device 100 canremain within the body. In one embodiment, a locking mechanism can beutilized to prevent rotation of the threaded members to ensure thedevice remains in the distracted state.

Once device is inserted and supporting the adjacent vertebral bodies, itcan be utilized to promote vertebral fusion. Following distraction, abone growth stimulant, such as autograft, bone morphogenic protein, orbone enhancing material, can be delivered into an open area definedwithin the device. In one embodiment, bone growth stimulant is deliveredafter insertion tools are disconnected. In another embodiment, bonegrowth stimulant is delivered through an open area between insertiontools. In a further embodiment, bone growth stimulant can be deliveredthrough a hollow chamber within the insertion tools. Device is capableof supporting in-vivo loads during the 6 to 12 weeks that fusion occursbetween the vertebral bodies. In one embodiment, openings 124 in baseplates 108 promote and allow for bone growth into and through the device100.

In some embodiments, when the device is implanted and in the process ofbeing expanded, as blocks come closer together the blocks compress thebone graft or bone fusion material that can be inserted inside device toforce the material out of the internal chamber of the device an in theadjacent vertebral end plates. This will enhance bone integration intothe end plates. Some bone material will remain within the cage, whichwill integrate and fuse the center of the cage to the top and bottom ofthe end plates. In certain embodiments, the bone material can beinjected into the device through one of the longitudinal holes in theproximal block of the device that does not have an actuation membertherethrough. This could be done with the inserter device or separateextended syringe. In some embodiments, the top and bottom base plates ofthe device can be coated to enhance bone integration.

In an alternative embodiment, a pin can extend vertical through thedevice to stabilize the proximal end of the device. Such a device couldbe expanded utilizing only a distal set of arm assemblies and wouldprovide only lordotic angles. Alternatively the pin could stabilize thedistal end of the device, which could then be expanded with a singlescrew and one or more proximally located arm assemblies to providekyphotic angles.

Although the various devices described herein are described as beingbrought from a compressed configuration to an expanded configuration byrotation of a threaded member, the devices can be distracted by anyother type of actuation member. In some embodiments, mechanisms otherthan threaded members can be used to distract the device. Suchmechanisms include, for example, a pop-rivet mechanism, a sardine keyand ribbon, a tourniquet and wire, a saw blade/ratchet, a zip-tie-likemechanism, piezo-electric inch worm motors and shape changing materialssuch as a shape member alloy or a conducting polymer actuator. Thesealternative locking mechanisms could be designed to make the devicebehave as if it were locked with a threaded member, preventing thedevice from being compressed as well as extended, or these mechanismscould afford the device the capability to ratchet upwards postimplantation if such action would benefit the patient or provideadditional therapy.

Various embodiments of implantation procedures for the disclosedembodiments of expandable intervertebral cage devices may be as follows:

Lumbar: A lumbar implant can be 8 mm in height, expandable to 14 mm inheight, with a length of 25-30 mm and a width of 10-12 mm. The implantcan be inserted through a minimally invasive tubular port that goesthrough the muscle of the lumbar spine and into the lumbar disc space.Prior to inserting the implant, the lumbar disc should be completelyremoved. Other embodiments for the lumbar spine include larger sizes foranterior, posterior, transforaminal, oblique lateral, and lateralinterbody fusions.

Cervical: A cervical implant can be 6 mm in height, expandable to 10 mmin height, with a length of 10 mm and a width of 6 mm. The implant canbe inserted after anterior cervical surgical exposure. The cervical discshould be completely removed prior to insertion of the implant.

Various embodiments of systems, devices, and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the present invention. It should beappreciated, moreover, that the various features of the embodiments thathave been described may be combined in various ways to produce numerousadditional embodiments. Moreover, while various materials, dimensions,shapes, implantation locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

What is claimed is:
 1. An expandable intervertebral cage device adaptedto be implanted into an intervertebral disc space in a patient's body,comprising: a first base plate having a first outer bearing surfaceconfigured to interface with a first vertebra of the intervertebral discspace; a second base plate having a second outer bearing surfaceconfigured to interface with a second vertebra of the intervertebraldisc space; a proximal block mechanically coupled to the first baseplate and the second base plate, wherein the proximal block comprisesinternal threading; a distal block comprising an internal passage; onlytwo arm assemblies, wherein a first one of the two arm assemblies isarranged on a first side of the device and a second one of the two armassemblies is arranged on a second side of the device, wherein each ofthe only two arm assemblies comprises: only a first rigid member and asecond rigid member that pivot with respect to one or more of the firstbase plate and the second base plate; the first rigid member pivotallyattached to the first base plate and the distal block; and the secondrigid member pivotally attached to the second base plate and the distalblock; and a screw arranged partially within the internal threading ofthe proximal block and passing through the internal passage of thedistal block, such that rotation of the screw relative to the proximalblock causes a change in distance between the proximal block and thedistal block, and a corresponding change in the spacing and lordosis ofthe device due to an expansion or contraction of the arm assemblies. 2.The device of claim 1, further comprising a rod passing through theproximal block and the first base plate to attach the proximal block tothe first base plate while permitting relative rotation therebetween. 3.The device of claim 2, further comprising a rod passing through theproximal block and the second base plate to attach the proximal block tothe second base plate while permitting relative rotation therebetween.4. The device of claim 1, wherein the first base plate and the secondbase plate each have an opening defined therein configured to allow bonegrowth into an open space defined by the device.
 5. The device of claim1, wherein the screw is threadedly coupled to the internal threading ofthe proximal block, and the distal block includes a non-threadedrotational coupling to which the screw is non-threadedly rotationallycoupled.
 6. The device of claim 1, wherein the screw includes a firstportion having a first diameter and a second portion having a seconddiameter.
 7. The device of claim 6, wherein the first portion of thescrew has a diameter adapted to pass through an opening in the proximalblock that includes the internal threading and the second portion of thescrew has an opening adapted to pass through an opening in the distalblock that defines the internal passage.
 8. The device of claim 1,wherein rotation of the screw relative to the proximal block furthercauses the arm assemblies to expand to angle the first base plate andthe second base plate relative to each other.
 9. The device of claim 8,wherein a distance between a proximal end of the first base plate and aproximal end of the second base plate remains constant as the armassemblies are expanded.